It is well known in the communications art that usable radio frequency spectra is becoming increasingly more scarce, particularly as the number of users of radio frequency based communication systems increases. When considering the various types of existing users of radio frequency spectra, which types include commercial broadcast, state, local, and federal governmental agency uses, cellular telephone uses, experimental, telephonic, and even trunked radio systems, it can be seen that available radio frequency spectrum is becoming increasingly more scarce.
Even though available spectrum of radio frequencies is limited, the need for radio frequency spectrum continues to increase as both the number of users of such spectrum increases and the types of uses of such spectrum increases as well. In many regions of United States, for example, the radio frequency spectrum set aside for so-called cellular telephone users has already been saturated such that cellular subscribers must frequently wait for a usable cellular radio frequency channel to become available. As the number of cellular subscribers continues to increase, users will experience increasingly longer delays in obtaining a usable frequency channel.
In addition to the well known cellular telephone service, there are currently in existence, plans for new two-way communications services that will themselves require additional radio frequency spectrum. As communications services increase, they will further crowd the air waves.
Accordingly, there exists a need to be able to more efficiently use the radio frequency spectrum that is currently available. Sharing existing radio frequencies between users, and between types of users, is perhaps the only way to accommodate the expected demand for radio frequencies. A problem with sharing radio frequencies is the interference one user who shares the same frequency with another user, causes to the other user or users. Accordingly, frequency sharing schemes that limit interference to users that share frequencies have been developed, some of which are quite complicated and require a significant amount of computer overhead. (Well known cellular and trunked radio systems both use computers to allocate frequencies between potentially competing users.)
At least one band of radio frequencies that are currently in use in the United States is set aside for use by so-called microwave point-to-point communication systems. This band of frequencies, exist generally between 1.8 and 2.0 GHz, and, by virtue of its high frequency, is usable only over relatively short distances and on a virtual line of sight communications path. Other bands of frequencies include at least the frequencies between 4 and 6 GHz. as well.
This frequency band, as well as other frequency bands, is currently in use by governmentally licensed subscribers that in any one area, at any one time, typically use only a very limited portion of the entire band and as such, much of the radio frequency spectrum in the band assigned to these types of users might be reused by other, unrelated services. Since existing users are entitled to a relatively uninterrupted use of this radio frequency spectrum (by virtue of the grant of the licenses of these users from various governmental agencies) any new users on this band of radio frequency spectra will likely be permitted to share such frequencies only if they can do so without adversely affecting existing users. Should new users decide to share these radio frequencies, they must be able do so in a way that permits them to use such frequencies but in a way that does not interfere with pre-existing users. Accordingly, a method and an apparatus that permits sharing of radio frequency spectrum between users of one type of communication system, with users of a second type of radio communication system might permit the limited radio frequency spectrum to be more efficiently used. Such a method and apparatus might dramatically increase the number of uses and users that could be accommodated in the limited radio frequency spectrum.